The running container jobs scripts S3_JWT_FILE needs to be removed on
exit because the resulting image is committed and we don't want the auth
token to leak permanently in the fs.
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/31093>
Set up "${S3_JWT_FILE}" also for container jobs, this can be useful in
case some jobs want to save something to S3.
Note that for container jobs setting the file /s3_swt in the
`default:before_script` section would not work: this wold be "too early"
because, when using ci-templates, the cbuild invocation switches the
root filesystem before executing FDO_DISTRIBUTION_EXEC, resulting in the
file becoming unavailable after the switch.
So set up the file exactly in FDO_DISTRIBUTION_EXEC, before launching
the actual container script.
Do this using a new trampoline script
.gitlab-ci/container/container_job_trampoline.sh so that in the future
other tasks common to all container jobs can be added there.
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/31093>
